Multistage spindle drive for converting rotary motion into linear motion

ABSTRACT

A multistep spindle drive is provided for converting a rotary movement into a linear movement with different speeds of withdrawal and extension. The spindle drive includes at least two threaded spindles, which telescopically mesh with each other and are in threaded connection with one another, and a nut. The inner threaded spindle is connected to a crank, and the nut is connected to a support wheel via a pipe. The internal threaded connection existing between the threaded spindles has a smaller diameter and a lower pitch than the external threaded connection existing between the outer threaded spindle and the nut. The speeds of withdrawal and extension are changed over based on the greater frictional force. A friction-increasing coupling member is arranged between the threaded spindles. The coupling member is spring-loaded and can be set for changing the friction.

FIELD OF THE INVENTION

The present invention pertains to a multistep spindle drive forconverting a rotary movement into a linear movement with differentspeeds of withdrawal and extension, including at least two threadedspindles with different pitches which telescopically mesh with oneanother and are in threaded connection with one another, wherein onespindle is connected to a drive element and another spindle is connectedto an output element via a nut and wherein the threaded spindles and thespeeds of withdrawal and extension can be changed over by frictionalforce.

BACKGROUND OF THE INVENTION

Such a spindle drive has been known from EP-A-0 552 129. The purpose ofthis arrangement is to perform the height adjustment of the supportwheel more rapidly, when this wheel is not loaded, than in the loadedstate. The spindle drive comprises two threaded spindles, which meshwith each other, are in a threaded connection with one another, and havedifferent pitches and diameters. The smaller inner spindle with thelower pitch is rotated by means of a crank, and is screwed into thelarger outer or hollow spindle. A nut, to which a support wheel isfastened via a pipe, is seated on the hollow spindle having the higherpitch. Due to the different pitches, the spindle drive has a fast motionand a load motion, which are changed over depending on the load bydifferent frictional forces in the threads. During fast motion andload-free spindle drive, the inner spindle is said to carry the hollowspindle due to the higher friction and rotate it in relation to the nut.As soon as a supported load appears and the better transmitted, slowerload motion is needed, the friction between the hollow spindle and thenut is said to become higher due to the load than the friction betweenthe inner spindle and the hollow spindle, so that the inner spindlerotates in relation to the stationary hollow spindle during load motion.The differences in friction in the spindles which are needed for thefast motion are said to be achieved by the differences in pitch anddiameter alone, which cannot always be achieved reliably and maintainedfor the long term in practice. It is also problematic that the threadbetween the hollow spindle and the nut is intentionally designed withoutself-locking. The consequence of this is, on the one hand, that thespindle drive may automatically withdraw under load in an undesiredmanner, and the position of the crank must therefore be compulsorilysecured. However, the operator may forget about this. On the other hand,the spindle drive operates only when the supported load actseccentrically from the spindle axis and it exerts an overturningmovement reinforcing the frictional force on the hollow spindle/nutpair.

Another spindle drive with fast motion and load motion for actuating asupport wheel for vehicle trailers has been known from DE-A 38 29 131.It likewise has an inner spindle and an outer spindle with differentpitches and diameters, which are guided concentrically one inside theother, but are not screwed to one another. The housing of this supportwheel comprises two parts, which are connected to one another via athread and form the outer or hollow spindle. The lower part is flangedstationarily to the vehicle trailer. The upper part is adjustable inheight by means of this thread and guides the inner spindle, which isconnected to the support wheel via a nut and a pipe section. Apretensioned friction clutch, by means of which the upper part of theouter spindle can be carried during the rotation of the crank, islocated on the crankshaft. The carrying takes place in fast motion, withboth spindles rotating and their strokes adding up. During load motion,the moment of friction is greater in the parts of the outer spindle thanin the friction clutch, so that only the inner spindle rotates.

SUMMARY AND OBJECTS OF THE INVENTION

The basic object of the present invention is to provide a multistepspindle drive, which makes possible easy handling and is able tofunction for a long time at low space and cost requirement.

According to the invention, a multistep spindle drive is provided forconverting rotary movement into a linear movement having withdrawal andextension with different speeds of withdrawal and extension. A spindledrive includes at least two threaded spindles each with differentpitches. The spindles telescopically mesh with one spindle being aninner spindle and the other spindle being an outer tubular spindle. Onespindle is connected to a drive element and another spindle is connectedto an output element via a nut. The speeds of withdrawal and extensioncan be changed over by frictional force. A friction increasing couplingmember is arranged between the threaded spindles.

The coupling member arranged according to the present invention betweenthe threaded spindles makes it possible to set the differences infriction necessary for the fast motion better and in a defined mannercompared with how this is possible with the differences in pitch anddiameter in the threaded spindles alone. The coupling member increasesthe friction between the threaded spindles to the extent that it isalways greater with certainty in the unloaded state than between thethreaded spindle and the output-side nut. Changes in friction, whichoccur during the operation and are due to wear, material, tolerances,dirt, and other effects, can be compensated with the coupling member.Moreover, the designer has a greater freedom of variation in selectingthe pitches, diameters, and materials of the threaded spindles. Thepresent invention ensures that the fast motion and the load motionfunction under all operating conditions and for the long term during thechange in load.

Various possibilities are available for designing the coupling member.It is preferably spring-loaded and its action is adjustable. Inaddition, it may act as a nut stop if designed as a threaded busharranged at the end.

To better secure the spindle drive against unintended withdrawal underload, the present invention provides for a suitable means in the area ofthe output-side threaded spindle and of the external threadedconnection. The lack of self-locking of the external threaded connectionis compensated as a result in a simple and reliably operating manner,and automatically. The operator no longer has to think of the supportsecuring and he no longer needs to actuate any extra securing means onthe crank.

Various possibilities are available for securing the spindle drive. Thepreferred embodiment with the friction-increasing flank profile offersthe advantage that it can act in a specific manner. With a flankflattening on one side, increased thread friction and quasi aself-locking is generated in the external threaded connection againstthe supported load, and this self-locking acts in the case of load onlyand does not hinder the extension and withdrawal of the spindle drive inthe fast motion. On the other hand, the change of speed and thechangeover of the spindle are improved. The spindle drive according tothe present invention operates reliably in the case of supporting forcesacting near the axis as well.

The spindle drive according to the present invention may have two ormore steps. It may be used for any purpose. A preferred field ofapplication is adjustable supports for vehicles or vehicle trailers.

Additional advantageous embodiments of the present invention aredescribed in the subclaims.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a longitudinal sectional view through a spindle drive in theform of a vehicle support;

FIG. 2 is an enlarged and cutaway representation of the spindle driveaccording to FIG. 1;

FIG. 3 is a cross sectional view through the spindle drive along lineIII--III in FIG. 2;

FIG. 4a is a cross sectional view showing the spindle drive in thewithdrawn positions;

FIG. 4b is a cross sectional view showing the spindle drive in theextended position;

FIG. 5 is a cutaway longitudinal sectional view through the flankprofile of the outer threaded spindle;

FIG. 6 is a cutaway longitudinal sectional view through the flankprofile of the internal thread connection.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a longitudinal section through a spindle drive 22, which isdesigned here as a height-adjustable support device for a vehicle or avehicle trailer. The spindle drive 22 may be used for any other purposeas well.

The spindle drive 22 is a two-step spindle drive in the embodimentshown. It comprises two threaded spindles 2, 4 meshing with each other,and a nut 6. The inner, drive-side threaded spindle 2 is provided at itstop end with a suitable drive element 15, preferably in the form of acrank here. The nut 6 rotating on the outer threaded spindle 4 isconnected to a pipe, which carries at the lower end an output element16, which is preferably designed as a rotatable support wheel here andis connected to the pipe 17 via an extension arm 25.

The spindle drive 22 is inserted into a housing, which is formed by,e.g., a cylindrical pipe 18. Flange plates or the like, acting asfitting parts 24 for fastening the spindle drive 22 to a vehicle or avehicle trailer, are arranged on the pipe 18. The shaft of the innerthreaded spindle 2 with the crank 15 projects from the top end of thepipe 18. The spindle shaft is fastened via a suitable pivot bearing 23with a pot-shaped support disk arranged under it to the cover of thepipe 18 and is held and guided centrally inside the pipe.

The pipe 17 connected to the nut 6 is telescopically guided in the outerpipe 18 and it preferably also has a cylindrical shape. As analternative, the two pipes 17, 18 may also be secured against rotationin relation to one another, which is possible by, e.g., an oval orpolygonal shape.

As is specifically shown in FIGS. 2 and 3, the inner threaded spindle 2and the outer, hollow threaded spindle 4 are connected to one anotheralong a common axis 1 via a so-called internal threaded connection 3.The inner threaded spindle 2 has external threads, which preferablyextend almost over the entire length of the spindle. The outer threadedspindle 4 has corresponding internal threads, which preferably extendover only part of the length of the spindle.

The hollow threaded spindle 4 has an external threaded connection 5, onwhich the nut 6 is linearly movable corresponding to the arrow 7 duringthe rotation of the outer threaded spindle 5. A rotary movementaccording to arrow 8 is introduced onto the inner threaded spindle 2via, e.g., the crank 15, and this rotary movement is converted into alinear movement 7 of the nut 6.

The nut 6 is secured against rotation, which can be ensured, e.g., bythe nonrotatable guiding of the inner pipe 17 connected to the nut 6 inthe outer pipe 18. As an alternative, the securing against rotation mayalso be achieved by increased friction of the pipe walls or by fixingthe support wheel 16.

In addition, a coupling member 9, which increases the friction on theinternal threaded connection 3, is arranged between the threadedspindles 2, 4. In the preferred embodiment, the coupling member 9 isdesigned as a threaded bush 9, which is in threaded engagement with theexternal threads 3 of the inner threaded spindle 2 and is guidedlongitudinally movably and nonrotatably in an enlarged, thread-freeopening at the lower end of the outer threaded spindle 4. For securingagainst rotation, the threaded bush 9 engages, with an outwardlyprojecting carrier 10, a slot-like recess 11 on the outer threadedspindle 4. A compression spring 12, which is tensioned between the frontend 13 of the outer threaded spindle 4 and a stop 14 located on thethreaded bush 9, is located on the circumference of the threaded bush 9extending beyond the front end 13 of the outer threaded spindle 4.

Together with the inner threaded spindle 2, which is in threadedengagement, the threaded bush 9 is pushed by the compression spring 12away from the outer threaded spindle 4. This leads to tensioning on theinternal threaded connection 3 and to the absorption of the backlashexisting between the two threaded spindles 2, 4. The frictional forceoccurring between the thread flanks of the inner threaded spindle 2 andthe threaded bush 9 as well as the outer threaded spindle 4 isincreased. The inner threaded spindle 2 and the nut 6 consist of metal,preferably steel. In contrast, the outer threaded spindle 4 consists ofa low-friction, tough plastic, e.g., POM.

The telescopic longitudinal movement of the outer threaded spindle 4 inrelation to the inner threaded spindle 2 is limited upward by thepot-shaped disk on the spindle shaft and a pivot and thrust bearing 23located on the head of the outer threaded spindle 4. The inner threadedspindle 2 is thus still able to rotate even when in contact. Thelongitudinal movement is limited downward by a stop at the end of theinner threaded spindle 2. The longitudinal movement of the nut 6 on theouter threaded spindle 4 is limited by the above-mentioned bearing 23 inthe upward direction and by the coupling member 9 or another stop in thedownward direction. FIG. 4 shows the spindle drive 22 in the withdrawnand extended positions.

The internal and external threaded connections 3, 5 are designed asmovement threads. They are, e.g., trapezoidal threads, which aredouble-threaded and have a reduced profile depth. The trapezoidalthreads may have increased backlash.

The internal threaded connection 3 has a lower pitch than the externalthreaded connection 5. In addition, the diameter of the internalthreaded connection 3 or of the inner threaded spindle 2 is smaller thanthe diameter of the external threaded connection 5 or of the outerthreaded spindle 4. The pitch angle of the external threaded connection4 is greater than the so-called angle of friction, so that the externalthreaded connection 4 has no self-locking in the case of normal flankgeometry of the trapezoidal threads. The external threaded connectionhas a size of Tr 30×16 P8 and the internal threaded connection 3 has asize of Tr 16×4 in the exemplary embodiment shown.

Due to the differences in pitch, the spindle drive 22 has a fast motionand a slow motion. The speeds are changed over depending on the frictionand load. The external threaded connection moves with the higher pitchin fast motion, as a result of which the nut 6 with the inner pipe 17and with the output element 16 moves up and down at increased speed,depending on the direction of rotation. The internal threaded connection3, which has a shorter stroke due to the lower pitch, but a better powerratio, rotates in slow motion. The output element 16 is moved rapidly upand down with the fast motion in the nonloaded state. The slow motion isswitched on when a supported load occurs, and it permits an ergonomicactuation of the spindle drive 22. The driving force to be applied orthe force of the hand is preferably essentially the same for bothspeeds.

The speeds are changed over depending on the friction and load. Due tothe differences in pitch and diameter as well as the force applied bythe coupling member 9, the friction is greater in the internal threadedconnection 3 than in the external threaded connection 5 of the threadedspindle 4 in the nonloaded state of the spindle drive 22. As a result,the inner threaded spindle 2 carries the outer threaded spindle 4 duringits rotation and rotates it in relation to the nut 6. The nut 6consequently moves linearly as shown at direction arrows 7 up and downin fast motion with the inner pipe 17 and the output element 16.

As soon as a supported load acting in the direction of the spindleappears, e.g., because the output element 16 reaches the ground, thisincreases the friction in the external threaded connection 5. A certainoverturning moment may also appear additionally because of the backlash.This moment is generated by the extension arm 25 and the eccentricaction of the supported load in relation to the spindle axis 1. Thefriction resistance in the external threaded connection 5 now becomesgreater than the friction resistance in the internal threaded connection3. The consequence of this is that the external threaded connection 5stops and the internal threaded connection 3 sets into motion, and theinner threaded spindle 2 rotates in the outer threaded spindle 4. Thisis the so-called slow motion, during which the nut 6 performs only aslow linear movement 7, while the torque to be applied to the innerthreaded spindle 2 is relatively low because of the smaller diameter.

The spindle drive 22 has a means for inhibiting the withdrawing movementunder load, which is arranged in the area of the external threadedconnection 5. As is shown in FIG. 5, the external threaded connection 5has a flattened flank angle on the thread flanks 19 that are the activeflanks under the supported load and the axial force 21. FIG. 5 showsthis on the external threads of the outer threaded spindle 4, in whichthe said thread flank 19 points downwardly toward the output element 16.

Increased frictional force, which leads to a kind of self-locking of theexternal threaded connection 5 under load, is generated by theflattening of the flank. The moment of friction or braking momentgenerated by the increased frictional force counteracts the drivingtorque applied by the supported load or the axial force 21 and preventsthe automatic withdrawal of the spindle drive 22 under load.

On the other hand, another consequence of this design is that thefriction in the external threaded connection 5 very rapidly becomeshigher under load than in the internal threaded connection 3, and thechangeover from fast motion to slow motion takes place. Contrary to thestate of the art, no overturning moment is needed for this in theexternal threaded connection 5. The increase in the frictional force andthe change in speed also take place under axial forces 21 which actclose to or in the spindle axis 1.

The flank angle to be selected for the quasi-self-locking depends on thedesign of the thread, the coefficient of friction, etc. In the practicalembodiment, the flank angle between the thread flank 19 and thehorizontal extending at right angles to the axis 21 has a value of atleast 40° and preferably 60°.

The flank profile of the external threaded connection 5 is preferablyasymmetric, so that the flattening of the angle and the increase infriction are present only on thread flanks 19 that are in contact withone another under load. The flank angle on the rear thread flanks 20 maybe steeper, corresponding to the shape of thread selected, and itequals, e.g., about 15° against the horizontal. As a result, there is noincreased friction resistance in fast motion during the load-freerotation up and down of the output element 16. The thread can bedesigned for this in the ergonomically favorable form.

Various modifications of the exemplary embodiments shown are possible.On the one hand, the threaded connections 3, 5 may have different threadshapes. Furthermore, the spindle drive 22 may have more than two meshingthreaded spindles 2, 4. Instead of the crank 15, it is possible to useanother drive element, e.g., even a motor or the like. Instead of thesupport wheel 16, the drive element may also have a support foot or thelike. This is advantageous, e.g., for supports of semitrailers.

The materials and friction pairings may be modified as well. They can bevaried in wide limits due to the coupling member 9, but the differencesin friction in the internal and external threaded connections 3, 5 whichare necessary for the fast motion and for the changing of speeds arenevertheless preserved. This also applies to the modifications of thedifferences in the pitches and diameters between the internal andexternal threaded connections 3, 5. There need not ultimately be anythread-related differences in friction in these threaded connections 3,5, and these differences may be generated by the coupling member 9alone. It is also possible to transpose the association of the spindlesand the differences in pitch.

Another variation is possible concerning the means for inhibiting theunintended withdrawing movement under load. Increased friction orself-locking may also be brought about by a spring element or tensioningelement, which acts, e.g., similarly to the coupling member 9. Inaddition, self-locking may be generated in the external threadedconnection 5 by means of changed friction pairings in the normal manner.

We claim:
 1. A multistep spindle drive for converting a rotary movementinto a linear withdrawal and extension movement with different speeds ofwithdrawal and extension, the drive comprising:a threaded spindle, witha threaded region having a threaded spindle thread pitch; anotherthreaded spindle with a spindle engaging threaded region and withanother threaded region having another threaded spindle thread pitch,said another threaded spindle thread pitch being different from saidthreaded spindle thread pitch, said another threaded spindle beingtelescopically connected with said threaded spindle to form a threadedconnection with said spindle engaging threaded region engaging saidthreaded spindle threaded region; a drive element, said threaded spindlebeing connected to said drive element; a nut engaged with said anotherthreaded region of said another threaded spindle; an output elementconnected to said another threaded spindle via said nut; and afriction-increasing coupling member connected to said threaded spindleand connected to said another threaded spindle for applying forcebetween said threaded spindle and said another threaded spindle forincreasing a frictional force at said threaded connection wherein one ofsaid threaded spindle and said another threaded spindle is an outerthreaded spindle and another of said threaded spindle and said anotherthreaded spindle is an inner threaded spindle.
 2. A spindle drive inaccordance with claim 1, wherein said threaded spindle is an outerthreaded spindle and said another threaded spindle with another threadedspindle thread pitch cooperates with a thread of said nut to provide anexternal threaded connection located between said another threadedspindle and said nut, said another threaded spindle being an innerthreaded spindle with said threaded connection being provided as aninternal threaded connection, said inner threaded spindle being guidedon said outer threaded spindle said internal threaded connection havinga pitch that is smaller than the pitch of the said external threadedconnection.
 3. A spindle drive in accordance with claim 2, wherein: saidouter threaded spindle has said external threaded connection on theorder of magnitude of Tr 30×16 P8 and a said internal threadedconnection on the order of magnitude of Tr 16×4.
 4. A spindle drive inaccordance with claim 2, further comprising: inhibiting means forinhibiting the withdrawing movement under load, said inhibiting meansbeing provided as part of said external threaded connection.
 5. Aspindle drive in accordance with claim 4, wherein: said externalthreaded connection has a friction-increasing flank profile in thedirection of the application of the load.
 6. A spindle drive inaccordance with claim 5, wherein: said flank profile has a thread flankwith an angle of at least 40°.
 7. A spindle drive in accordance withclaim 6, wherein: said flank profile has a thread flank with an angle ofapproximately 60°.
 8. A spindle drive in accordance with claim 5,wherein: said external threaded connection has thread flanks ofdifferent flank angles including a thread flank that is in a non-drivingstate under supported load which is steeper than saidfriction-increasing flank profile.
 9. A spindle drive in accordance withclaim 1, wherein: said coupling member includes a spring-loaded threadedbush on said inner threaded spindle.
 10. A spindle drive in accordancewith claim 9, wherein said threaded bush includes a carrier, said outerthreaded spindle having a fitting radial recess, said threaded bushengaging said fitting radial recess.
 11. A spindle drive in accordancewith claim 10, wherein:said carrier is a radially outwardly projectingcarrier; and said tubular outer threaded spindle has a slot, definingsaid fitting radial recess, which extends axially in parallel and isengaged by said radially outwardly projecting carrier.
 12. A spindledrive in accordance with claim 1, wherein: said friction-increasingcoupling member includes an axially acting compression spring, saidthreaded bush having a stop, said axially acting compression springbeing tensioned between said front end of said outer threaded spindleand said stop of said threaded bush, guided on a circumferential surfaceof said threaded bush.
 13. A spindle drive in accordance with claim 12,wherein: said threaded bush includes a radially outwardly projectingcarrier; and said tubular outer threaded spindle includes a wall with asaid slot, slot extending axially in parallel to and engaging saidradially outwardly projecting carrier of the said threaded bush.
 14. Aspindle drive in accordance with claim 1 wherein: said inner threadedspindle and said nut are formed of metal and the said outer threadedspindle is formed of a low-friction plastic.
 15. A spindle drive inaccordance with claim 14, wherein: said metal is a steel or steel alloy.16. A spindle drive in accordance with claim 1, wherein: said driveelement includes a crank, and the said output element includes a supportfoot or support wheel.
 17. A spindle drive in accordance with claim 1,wherein: said spindle drive is as an adjustable support.
 18. A spindledrive in accordance with claim 17, wherein: said support is a supportwheel.
 19. A multistep spindle drive for converting a rotary movementinto a linear withdrawal and extension movement with different speeds ofwithdrawal and extension, the drive comprising:an outer threadedspindle, with an outer threaded region having a outer threaded spindlethread pitch; an inner threaded spindle with an inner threaded regionand with another threaded region having another thread pitch, saidanother thread pitch being different from said outer threaded spindlethread pitch, said inner threaded spindle being telescopically connectedwith said outer threaded spindle to form a threaded connection with saidinner threaded region engaging said outer threaded region; a driveelement, said inner threaded spindle being connected to said driveelement; a nut engaged with said another threaded region of said anotherthreaded spindle at a nut threaded connection; a friction-increasingcoupling member connected to said outer threaded spindle and connectedto said inner threaded spindle for applying force between said outerthreaded spindle and said inner threaded spindle for increasing africtional force at said threaded connection; and an output elementconnected to said outer threaded spindle via said nut, said outputelement having a load state and a no load state wherein in said loadstate a frictional force at said nut threaded connection is greater thana frictional force at said threaded connection for changing the speedsof withdrawal and extension.